For lapping components such as the gears of gearboxes, it is known to place the gears with a slight axial clearance into cassettes which are held by a cardan-type suspension device during lapping, with an antirotation device being provided for preventing the gear from rotating under the effect of the lap. The main drawbacks of this method of lapping are that it is necessary to place each gear to be lapped in a suitably designed cassette, that the cassette and its suspension have many components susceptible to wear, that the antirotation device which angularly immobilizes the gear while it is being lapped has to be sized as a consequence of the torque transmitted therefrom and that in the case of gears in which the reference faces are set back, the faces via which the gear contacts the cassette do not coincide with its reference faces.
Another known centering and clamping device specially designed for lapping gears comprises a fixed stop against which the gear to be lapped is applied directly by a rest on which a set of concentric fluid pistons acts. This set comprises a first fluid piston with a large stroke relative to its cylinder, and a second fluid piston interposed between the rest and the first piston and having a short stroke relative to the latter. The stroke of the first piston is fixed and selected so that when the first piston is fully extended and second piston is fully retracted, a slight amount of play less than the stroke of the second piston remains between the gear and the rest and/or the fixed stop. With the gear thus angularly immobilized by an anti-rotation system, the lap, driven in rotation, is then engaged inside the gear and the lap is expanded until a predetermined braking torque is established between the lap and the gear, indicating that the abrasive stones of the lap are in contact with the bore of the gear, and the latter is then centered relative to the lap. The second piston is then extended so that the gear thus centered is clamped by bearing against the fixed stop, with a view to its being lapped.
This known device, while offering advantages relative to the cassette device (fewer wearing components, the possibility of making the gear/rest and gear/stop contact surfaces coincide with reference surfaces which are set back on the gear) does however exhibit the drawback that the stroke of the first piston is fixed and predetermined, so that on each change from a gear having a given axial thickness to a gear having a different axial thickness it is necessary also to change the stop to replace it with a stop having a complementary axial size.